(1) Field of the Invention
This invention relates to bus bars, especially relatively small or miniature bus bars. More particularly, this invention relates to multilayer bus bar assemblies, and the method of manufacture thereof, wherein the bus bar assembly incorporates capacitive elements between layers of bus conductors to provide high capacitance bus bars.
(2) Description of the Prior Art
Conventional bus bars of relatively small or miniature size have been known in the art for a number of years. These devices are used for power and/or signal distribution in many systems, such as, for example, computer back panels and integrated circuit systems. Such prior art multilayer bus bars comprise at least two conductive plates (usually in the form of elongated strips or bars of copper) separated by an insulating film. A typical prior art bus bar of this type may use copper conductors having a thickness of about 10 mils, and the overall dimensions of the bus bar may be from about 0.019 to 0.120 inches thick, from about 0.150 to 0.200 inches wide and range in length up to about 16 inches. Typically, the separating insulating layer is a plastic dielectric film such as the polyester material known as MYLAR. The MYLAR separator layer and the conductive plates are bonded together by an adhesive. Prior art bus bars of this type have relatively low capacitance.
It has also been suggested in the prior art to construct miniature multilayer bus bars of this type having high capacitance. It has been proposed to achieve the objective of high capacitance. It has been proposed to achieve the objective of high capacitance by incorporating capacitive elements in the bus bar assembly between the conductive layers of a multilayer bus bar. Reference is hereby made to U.S. Pat. Application Ser. Nos. 950,265 and 950,266, both of which are owned by the assignee of the present invention, and both of which relate to multilayer bus bar systems having high capacitance elements between conducting layers of the bus bar assembly. These high capacitive elements are thin layers or chips of dielectric material with opposite surfaces coated with a thin, integral and continuous film of conductive material. Some or all of these prior art systems have included the feature of the use of conductive adhesive to bond together the multilayer bus bar assembly and provide the necessary electrical contact between the conductive layers of the bus bar assembly and the conductive outer surfaces of the capacitive elements between the bus bar layers.
While these prior art systems are workable, the use of the conductive adhesive imposes serious processing limitations, because considerable care must be exercised in the manufacturing process to make sure that a short circuit path is not established between the conductive layers of the bus bar by the conductive adhesive. Any such short circuit, whether it occurs during the manufacturing process or whether it occurs during handling or use of the device after manufacture, will destroy the effectiveness and utility of the bus bar. Thus, in the manufacturing process, great care must be exercised to make sure that the conductive adhesive (which is typically a thermoplastic material) does not leak out of the assembly to cause electrical leaks or short circuit paths with high dissipation factors. Thus, only relatively low pressures (on the order of 10-15 psi) can be employed in assembling these prior art devices, encapsulation techniques are limited, and limits are imposed on the thickness of the device in that the layers cannot be squeezed together to produce as thin a device as might be desired. The presence of the conductive adhesive in the finished device also poses a continual problem of possible establishment of a short circuit path during the lifetime of the device.